Abstract: An end effector device is mounted on the arm of a robot for movement through a predetermined motion relative to control axes of the robot under control of a robot controller which also controls a driver of the device to apply at least one variable programmed drive force to a first part relative to a second part at a work station. Preferably, the driver includes a screwdriver which is driven by an electric motor which, in turn, is controlled to apply a variable programmed torque at a variable programmed speed to a screw. The screwdriver and its electric motor are mounted on a slide for movement between extended and retracted positions relative to a base of the device. An air cylinder is coupled to the slide and is controlled to linearly move the slide so that the screwdriver applies a variable programmed axial force to the screw. The driver has a drive compartment formed therein which is maintained under a negative pressure for receiving and retaining the screw.